In today's regulated environment, power utility companies charge consumers or end users according to a policy that encourages energy conservation and assesses the cost for acquiring and maintaining extra power generating equipment to meet peak demands against those end users who create the peak demand. Accordingly, power utilities will typically charge customers for electricity at a first rate for electricity consumed below a first predetermined level, and at a second rate for electricity consumed between the first predetermined level and a second predetermined level. If electrical power consumption exceeds the second predetermined level, a penalty or surcharge is charged to the end user. This surcharge accounts for the fact that the utility had to acquire and maintain extra power generating equipment to meet those periods of unusually high or peak demands.
In order to avoid peak demand charges imposed by the power utility, power end users have employed automatic control systems which monitor power consumption within their facilities and then modify the on/off status of power consuming loads within the facility to maintain power consumption below a predetermined value or setpoint. These systems have typically taken the form of add/shed control systems. The systems are designed to shed loads as power consumption approaches a predetermined level or setpoint which is chosen by the end user. As power consumption begins to fall away from this setpoint, previously shed loads can be added back to operational status so that it may be turned on and utilized by the and user.
There are different types of add/shed control systems. A more common type of add/shed control system establishes a prioritized load order wherein the load having lowest priority will be shed first and the load having highest priority will be shed last. In such a system, if loads can be added back online, the load having the highest priority will be added first and the load having the lowest priority will be added last.
Today's energy saving and cost reducing strategies typically control a building's power consumption based on a programmed setpoint. This type of strategy uses a electrical load shedding setpoint. When the current electrical consumption reaches that setpoint, or is forecast to reach that setpoint, an electronic controller starts reducing electrical loads until the current power consumption is maintained below the setpoint. This type of strategy works well for reducing total kW (kilowatt) consumption and reducing peak demand.
There are many types of strategies as to what loads are shed during this power reduction mode. For example, in offices, the strategy may allow the temperature in the building to rise a few degrees, or in a supermarket, the strategy may drop off some lighting and refrigeration loads. No matter which strategy is used, the basic controlling factor is the setpoint that allows only a certain amount of kilowatts to be used within a specified time window. When the allowed amount is exceeded, or is predicted to be exceeded, the control strategy starts to turn off power consuming items until the consumption is maintained within the allowed amount. Some schemes use prioritizing selections for shedding and adding loads, and use methods for predicting or forecasting the anticipated need for load shedding. Examples of load shedding control schemes are described in U.S. Pat. Nos. 4,075,699; 4,216,384; 4,337,401; 4,916,328; 5,543,667; 5,414,640; 5,644,173 and 5,598,349.
There is an inherent drawback to these types of strategies. That is, if an apparatus or device is consuming power, it is operational for a reason. For example, in a supermarket, refrigeration is the largest power consumer, consuming about 40% of the supermarket's total electrical usage. When refrigeration is shut off for energy savings, it may be detrimental to the refrigerated product. This type of strategy can affect such things as increased product loss and reduced shelf life. If load shedding is implemented without safeguards, some of these energy saving strategies would hamper the ability to maintain food safety standards.
In this regard, two important considerations for refrigerated storage of food in the supermarket are food safety and “shrink” (product loss due to poorly maintained product). The FDA and the USDA specifies that for certain food products to be safe for public consumption, the supermarket refrigeration must maintain the product's core temperature below 41° F. If for any reason the product's core temperature rises above 41° F., food-borne pathogens begin to grow. Such pathogens include eColi and salmonella. Therefore, the supermarket or cold storage facility must maintain an adequate “cold chain” for food safety reasons.
Although food safety is not a concern until the product's core temperature rises above 41° F., shrink can occur at a much lower temperature. For example, if ice cream rises above 5° F. for a prolonged period of time, its condition deteriorates and it is no longer sellable. Although the ice cream is safe to eat, the supermarket has lost the ability to gain profit from the product sale. Almost every product in the cold chain has a shrink temperature that is far below the food safety temperature, however, both are important to the supermarket owner/operator.
These two concerns have limited the energy engineer's ability to implement an effective load shedding strategy in a supermarket/cold storage facility. As well, in an office environment, increasing temperature setpoints can result in an uncomfortable work environment, thus impacting efficiency and production. Almost without exception, today's control strategies save energy at the cost of a desired condition (cold products, cool or warm offices, extra lighting, etc.).
In the past few years, the electrical power industry has started deregulating in many states. Deregulating electricity will allow consumers to purchase electricity as a commodity on the spot market. Under most of the current deregulation legislative approaches, an end user is given the opportunity to purchase electric power from many legitimate power generating companies willing to supply electric power to the end user's geographic region. The increased competition will ultimately reduce the end user's energy cost. As competition increases, power generators are expected to offer customers various pricing plans, including, for example, plans based on volume and term commitments, and/or on peak/off-peak usage.
It is anticipated that the local distribution company facilities of the local electric utility would continue to be a regulated monopoly within the region it serves. These facilities are primarily the lines and other equipment that constitutes the local power grid over which electric power is delivered to the end user, having been delivered to the grid by generating plants within the local utility service area or by other utilities' grids interfacing with the local utilities grid.
The electric utility primarily relies on meters at customer cites to apprise the utility of how much energy the customer has taken from the local utility's grid. Many of these meters can measure the volume of energy used, the highest volume used during any hour throughout a monthly billing cycle (peak demand), and the volume used in every hour of the monthly billing cycle, or as short a period as every 15 minutes during this cycle. Some meters, such as those used by commercial end users, can measure all of the above. Other meters measure only monthly total electrical usage and peak demand. Meters servicing residential customers often measure only total electrical usage for the month. More sophisticated meters now available enable the local utility to monitor the end user's actual energy usage electronically.
Currently, using these more sophisticated meters, the local utility can continuously monitor the end user's actual energy usage by taking readings every 15 minutes throughout the day. The local utility records that energy usage data and applies its applicable tariff rate to produce a bill for the end user. These tariffs set forth specific rates to be charged to different classes of customers. Some tariffs call for different rates depending on time of use (peak v. off-peak pricing). As deregulation progresses, these same sophisticated meters will allow competing energy providers to offer end users multiple pricing plans and contractual arrangements, such as being configured for time of use, volume and term commitments, etc.
It is anticipated that deregulation will be implemented by power pools or exchanges to make the wholesale market of electricity as a commodity more efficient and to give energy marketers (marketers not affiliated with a local utility) a reasonable chance to compete. The California Public Utilities Commission, for example, has proposed a power exchange to which the three largest in-state electric utilities must sell all their generated power and from which they must buy all the power they need for distribution to their end user customers. Other power generators, utilities, resellers, traders and brokers also buy and sell power through this exchange. In operation, each day the exchange will assess the power supply requirements for the next day for all the end users. The exchange will have power generators, local utilities with generating capacity, resellers and traders submit bids for specified quantities of power to be delivered to the power grid during each hour of the next day. The exchange will then match its assessed needs for power during each hour of the next day starting with the lowest priced power first until it has identified sufficient power supplies for each hour to meet its anticipated demand. The price of the final bid to meet the anticipated demand sets the market price for each hour.
Another system for implementing a commodity spot market system for electric power is described in U.S. Pat. No. 6,047,274. In this system, a “moderator” collects bid information from electricity providers, sorts the bid information according to the rules of an auction, and may further process this bid information, for example, to select electricity providers for particular end users. The provider selection information may include, for example, a prioritization of the providers in accordance with their bids and/or the designation of a selected provider as a default provider. The moderator then transmits selected portions of this information to control computers associated with each end user or group of end users, as well as to participating providers. Each control computer receives the rate information and/or provider selection information from the moderator that pertains to the end user or group of end users with whom the control computer is associated.
From the list of all providers providing bid information to the moderator, each control computer can select one or more providers from whom the participating end user will be provided electric power. The end user can change that selection at any time. After each new bid is submitted by a provider and is processed by the moderator, the rate and/or provider selection data will be transmitted to the relevant control computers and rate information can be distributed to some or all of the providers in order to implement the auction. All providers will then have the opportunity to submit a lower or higher bid for any end user or group of end users to whom they wish to supply electric power. Throughout the bidding process, providers can compete to supply electric power to end users based on available capacity, delivery destinations, volume discounts, peak period requirements, etc. The electric power bids and resulting contracts can be for a preselected kilowatt amount over a preselected unit of time, and number of units of time.
Once a provider has been selected, the moderator of the power exchange can monitor the actual electricity consumed by the user by collecting meter readings. The aforementioned sophisticated meters can transmit usage reports to the moderator every 15 minutes or more or less often. It is anticipated that in the future it will be possible to transmit energy usage in even smaller increments of time than 15 minutes (i.e., near real time). End users can easily make economic choices among competing providers.
Rather than the control computer of each end user selecting the provider with the lowest rate, the moderator can perform this function. The moderator control computer selects the provider's offering the lowest rate at each time block and provides that rate to each end user, i.e., setting or posting the current spot market price.
Other systems for implementing a commodity market for electrical power are disclosed in U.S. Pat. Nos. 5,894,422 and 5,237,507.
The present inventor has recognized that deregulation of electric utilities creates a desirable opportunity for a new load shedding strategy that could take advantage of this new method of buying electricity as a commodity on the spot market.
The present inventor has also recognized that in a deregulated electric utility market it would be desirable for supermarkets and other users of power for refrigeration to implement an effective load shedding (power saving) strategy for refrigeration equipment. The present inventor has recognized the desirability of providing a load shedding strategy for refrigeration equipment which is effective to reduce utility costs while maintaining product quality.